Sugarcane bacilliform virus encapsidates genome concatamers and does not appear to integrate into the Saccharum officinarum genome

Summary. Sugarcane bacilliform virus (SCBV) DNA molecules larger than the complete genome length of 7.6kbp were detected in infected plants and in virions. We have confirmed that these high molecular weight nucleic acids were open circular DNA and viral in origin. Due to their open circular conformation, accurate size determination of the DNA molecules was not possible using conventional electrophoresis. Using field inversion gel electrophoresis (FIGE), however, the DNA appeared to increase in genome size increments, with sizes ranging from 1 to 4 genomes (31kbp) detected. The DNA was packaged into virions, which may explain the observation of purified virions with lengths corresponding to one, two or three times the modal length of 130nm. The DNA products were possibly concatamers formed during replication as a result of a terminal overlap on the sense strand, and were shown to be overlapped individual genome-length molecules and not covalently-bonded continuous DNA strands. Southern analysis indicated that SCBV sequences are not integrated into the sugarcane genome and that the high molecular weight DNA observed in the sugarcane accessions analysed represents SCBV concatamers.